In the past, in order to form a tire having a tread portion provided with a land portion (block, lug, or the like) in a tire tread portion, a manufacturing method in which a vulcanizing mold with its inner peripheral surface formed with concavities and convexities corresponding to blocks and lugs and a green tire formed by attaching a green tread to a green casing are prepared, and the green tire is loaded in the mold for vulcanization, then rubber of the green tread is flowed into the concavities while being pressed by the convexities of the mold has been generally used.
Although a carcass that forms a tire skeleton structure and a belt for reinforcement are disposed on desired positions inside the green casing, they may be locally pressed by the convexities of the mold or moved with the rubber flowing into the convexities, which may cause the belt, or the like, to be shifted from its original position and distortion may occur. In particular, tires mounted on agricultural vehicles used in the paddy field or the soft ground, or the like, or mounted on construction vehicles driving on the rough ground have high lugs rising from the outer surface of a tire body to obtain a high traction, which allows a lot of green tread rubber to be flowed into the concavities of the mold. Thus distortion of the carcass and the belt becomes pronounced and the tire performance may be affected.
As a technique for solving such a problem, for example, JP2012-045917A (PTL 1) illustrates a method in which a plurality of vulcanized lug members corresponding to lugs are previously loaded in a vulcanizing mold, then a green casing, which serves as a tire body, is loaded in the vulcanizing mold, and after that the lug members are vulcanized with a green casing to bond with one another. By this method, flowing of rubber into portions corresponding to the lugs of the mold is avoided, thus distortion of a carcass and a belt can be suppressed.